Fluid couplings are known. When used in a vehicle driveline, an impeller of the fluid coupling is generally connected to an engine and a turbine of the fluid coupling is generally connected to a transmission. When the vehicle is stopped, the impeller spins with the engine and the turbine does not rotate. Significant engine idle losses may occur when the vehicle is stopped because the fluid coupling is a relatively stiff connection. This means that the engine must use additional power to keep the impeller spinning when the turbine is stationary.